https://www.salliemae.com/about/investors/debtasset/
The student loans themselves are assets (the fit the above definition), my point is that they themselves are not asset based like a house or car loan.
Sallie Mae's use of the term "asset" here might be slightly misleading, but being essentially part of the government they can get away with it.
https://www.salliemae.com/about/investors/debtasset/