I own one. he can’t go 50 miles or even 5.. one lap around the block and he’s out of gas. he’s just over a year old.
They are made for tracking no doubt, and that is how they find themselves lost. But covering 50 miles? um no.
70 lbs is also normally a very over weight basset.
I’m with you, he should keep him but be aware of missing/lost dog ads in case he has to return him.
Pic he posted looks more like a Beagle/Basset mix.