Section 14.4 (#FTGRA) of P5 says:
"Three kinds of content may be supplied inside a figure element: the element <head> may be used to transcribe (or supply) a descriptive heading or title for the graphic itself [. . . .] Figures are often accompanied not only by a title or heading, but by a paragraph or so of commentary or caption. One or more <p> or <ab> elements may be used to transcribe any caption or discussion of the figure in the source[.]"
I read "by a paragraph or so of commentary or caption" to mean "by a paragraph or so of commentary or by a caption". If that's what's intended, then we need to provide guidance on how to distinguish a title or heading (for which you use <head>) and a caption (for which you use <p> or <ab>). The first example of <head> in use looks much like a caption to me.