At a guess, there are a few things going on here.
1.) I am sure WIS discounts CS% for catchers who were part-timers. Which makes sense. You certainly don't want a guy who threw out 1 runner in 1 attempt to have a 100% CS as a regular catcher. They may give the guy an A+ arm, but the underlying percentage they use is almost certainly adjusted (on a related note, the A+ arm for Bert Campaneris in 1965 is an error. Campy famously played all 9 positions in 1 game that season, and did not throw out any runners in his one inning as a catcher. But he did have 1 assist in that game while playing other positions, so he "looks" like a strong-armed catcher from the perspective of assists/game.)
2.) More to the point, the guys running on Lavalliere weren't exactly a whos-who of basestealing threats from the era. Among the players he "caught" stealing were Bret Boone (2 SB in 5 attempts that season), Dean Palmer (11/21), Greg Gagne (10/22), Greg Litton (0/1), Juan Bell (6/13), Omar Vizquel (12/26), Reggie Jefferson (1/4). Whereas the guys who were successful were, as a rule, better basestealers: Albert Belle (23/35), Chad Curtis (48/72), Ruben Sierra (25/30), David Hulse (29/38), Kirk Gibson (14/21). I'm cherrypicking some data here - there were certainly a few counterexamples - but the point is it would not be realistic to take his 75% CS rate against a group of guys who were not, as a rule, good SB men...and have that translate into 75% throwing out Vince Coleman, Tim Raines, et al.
3.) Also on the small sample size point, at least 2 of his CS (could have been more, I didn't look carefully) were players who were thrown out at home as part of a doublesteal. The catcher gets an assist on that play if he throws the ball to (say) the SS who then returns it to home, but it's not clear that he deserves to be credited with a CS. In a full season, that stuff washes out, but in a small number of games it can make you look better than you are.
4.) Lavalliere in his career never had another performance like that. Again, small sample sizes.
All of which is to say, I am comfortable with downgrading him.
Add on to that the point that uncleal makes, which is that many owners set SB to 0 for anyone who was not a frequent and successful thief. And Sparky takes into account, in some fashion, the opposing catcher's arm before calling for a steal. So in WIS, Lavalliere probably only has the best of the best running against him. There's no way he's going to throw out the elite basestealers in MLB history at a 75% rate.