That is overstating it a bit; there are mentions decades (but not centuries) after his reported death.

https://en.m.wikipedia.org/wiki/Historical_Jesus has a good overview of the non biblical sources.

You're right, after looking it up it was Muhammed who we have records mentioning either during life or within ~30 years[1]. For Jesus it definitely came after.

1- https://i.reddit.com/r/AskHistorians/wiki/faq/religion#wiki_...