I digitale sammenhenger ville jeg foretrukket å si "å legge ut".
I would prefer to say "å legge ut" when talking about a blog.
It seems 'å legge ut' is about 3-8 times more common than 'å poste' in this context, so you're completely right. There is nothing wrong about using a less common phrase.
Wow, where did you check that? It's good to know that I can be right about my own language :P We normally use "å poste" about posting a letter, so it's not directly wrong, but using "å poste" in this situation is often as a loanword from the english "to post", and with the english intonation. Therefore I think a learning site should try not to use it.
I just searched for the phrase "poster på bloggen" on a serach engine and compared the number of results with "legger ut på bloggen", which was about 7k vs 30k results. I think I will change it, as you said it's better to translate to a new phrase rather than a loaned meaning.