When filtering for basic rules it includes all of the classes, races and variants from the PHB and DMG. Including variant human and the like, and the source book includes everything from the PHB.

As opposed to correctly filtering to the basic rules.
https://media.wizards.com/2018/dnd/downloads/DnD_BasicRules_2018.pdf
https://dnd.wizards.com/products/tabletop/players-basic-rules

What are you trying to filter? An example of a non-basic rules entry that appears when filtering by basic rules might help the issue (if there is one) get diagnosed.

I've just filter magic items, spells and monsters by Basic Rules source and I'm not getting any non-SRD/Basic rules results

https://www.dndbeyond.com/sources/basic-rules

There's no filter on that page or any subsequent pages in that source, so I'm still not sure what you're referring to.

Unless you're referring to the fact that the Basic Rules source contains content from the SRD? That's intentional; D&D Beyond combines the SRD in with the basic rules in order to simplify things as the SRD isn't designed as a gameplay document, but a games design document for making OGL compatible games.

Quote from Davedamon >>

There's no filter on that page or any subsequent pages in that source, so I'm still not sure what you're referring to.

Unless you're referring to the fact that the Basic Rules source contains content from the SRD? That's intentional; D&D Beyond combines the SRD in with the basic rules in order to simplify things as the SRD isn't designed as a gameplay document, but a games design document for making OGL compatible games.

 The OP posted links to the Basic Rules from media.wizards.com and from dnd.wizards.com so I’ll simply linked the the Basic Rules on this website so they could find it.

I really should pay closer attention to who I'm replying to and not just what.

Quote from Davedamon >>

I really should pay closer attention to who I'm replying to and not just what.

 Lol

No worries friend.

I am saying that selecting the Basic rules from character creation, or directing players to Basic rules here... doesn't give the basic rules, it gives a hybrid.

Nor does it say "hey this isn't the basic rules, we have merged the SRD and the basic ruleset". I believe it would be worth renaming it to something else if the intention isn't to use the Basic rules.

Now of course people may respond with "why does this matter", firstly there is an accuracy thing, secondly because I was running a simple first game for disabled teens and it struck me when one of them brought in a D&D beyond charactersheet they had created with the "basic" rules and had a ranger (then conundrum, another player I had told to stick to basic and not PHB was upset, and the player who brought the Ranger had been accused of lying when they said they used the Basic rules).

Quote from TheGleefulGrognard >>

I am saying that selecting the Basic rules from character creation, or directing players to Basic rules here... doesn't give the basic rules, it gives a hybrid.

Nor does it say "hey this isn't the basic rules, we have merged the SRD and the basic ruleset". I believe it would be worth renaming it to something else if the intention isn't to use the Basic rules.

Now of course people may respond with "why does this matter", firstly there is an accuracy thing, secondly because I was running a simple first game for disabled teens and it struck me when one of them brought in a D&D beyond charactersheet they had created with the "basic" rules and had a ranger (then conundrum, another player I had told to stick to basic and not PHB was upset, and the player who brought the Ranger had been accused of lying when they said they used the Basic rules).

 Most people do not make the distinction since it is all published for free by WotC. 

Thank you for your feedback, TheGleefulGrognard! We appreciate you sharing your experience, and your suggestions on how we could improve our filtering.