Disclaimer: Individual users are free to vote as they please - if these specific users haven't seen fit to leave a comment on your question, it's unlikely they'll feel compelled to answer here either, and ultimately only they know why they voted the way they did. I haven't voted on your question either way at the time of writing this answer.
You write in your question that you think
Thermal power means heat after considering all the heat emitting mechanisms whilst thermal radiation is just the heat emittance due to radiation.
but it is left entirely unclear what other "heat emitting mechanisms" you think a black body in this context has. The post by Daniel Sank you cite makes no mention of any other mechanisms, and is pretty clearly focused on radiation throughout. Your question comes across as nitpicking a minor choice of words rather than asking something interesting about physics. This would suffice for me to categorize it as "not useful", one of the generic reasons to downvote a post.
(Usually the following doesn't lead to downvotes on its own, but since you asked for feedback I might give it as well:) Also, your opening sentence:
In Concept's of Physics part-2 by HC-Verma, it is written on page 87 right under section 28.10 it is written
is not a great first impression: There's a superfluous apostrophe in "Concept's", a superfluous hyphen in "part-2" and a superfluous hyphen in the name "HC-Verma" (should be "H.C. Verma" in standard English orthography), and you've doubled the "it is written" part.