Oil cooler line off

Hello! I installed a new radiator in my 1997 Eldorado recently, and after the install I fired it up, let it get up to temperature, and drove it with no issues. However, I drove it for a second time yesterday, and got a low oil pressure light about a mile into my drive. Luckily I was near home, I pulled in and saw it spilling out oil. The lower oil line to the bottom of the radiator/oil cooler blew off. The fitting was still attached to the radiator, but the line itself was dangling.

I am going to put a new oil line on this weekend. My guess is that the fitting just wasn't seated correctly - is this most likely the case? Anything else I should look for when installing the new line? Thank you in advance!