Hmm... perhaps DnD beyond  MIS-uses a full cylinder icon for radius, perhaps & hopefully-not.

Often in technical symbology, a radius is written/drawn as  ;

1   r.

2   top-down-view of a circle with a dot and a line only drawn half-way from the dot to an edge, with a symbol next to the line,

3   a cylinder with the same, on it's top-oblong section  (not a BLANK top)

the D&D Beyond sheet seems to have a cylinder, withOUT the line on the top, which would suggest a cylindrical space, and so the DIAMETER,

without FURTHER notation,

or,.. hopefully, someone's just chosen the wrong icon, when they were programming the entry for Moonbeam?

 or,.. i guess, someone incorrectly typed-in 5 instead of 10,.. but how does ones mistake doing that?

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Either way, i'm having to make a note on my sheet to not forget that Moonbeam's  NOT a 5' diameter.  

Easily spotted, easily fixed.