Correct. The parent of your post should have written "10 trillion kelvins", "10 terakelvins", or "10 TK". The article wrote "Temperatures there reach an astonishing 30,000-50,000 kelvin" instead of "kelvins" (or better yet, 30–50 kK).
The only exception regarding capitalization is that the person Celsius is capitalized in the multi-word unit "degree(s) Celsius", and the pluralization is on "degree".
Very few people use the unit kelvin correctly. ( https://www.reddit.com/r/Metric/comments/126sniq/everyone_mi... )
The only exception regarding capitalization is that the person Celsius is capitalized in the multi-word unit "degree(s) Celsius", and the pluralization is on "degree".