All (or nearly all) of his routes continue onwards from the other airports, 4-legs .. so he is not using the routes for the sole purpose of getting the slots but to route his planes elsewhere as the home airport of his is already fully utilized.
So basically he's just repositioning his planes and flies pax from those airports to other places. Kind of like HUB .. but just not that economical as the first and last sector are running on low LF - but the only way for him to grow as the IAH is already full.
...so not using the slots on purpose to just to keep the slots, he is actually trying to make money with all of the zillion planes he has. And not comparable to the other case we had recently.
Some airlines tend to do this and the downside is that some routes (these 'repositioning routes') become overcrowded. There is no "admin ruling" to this as it's part of his strategy and it's not made in the purpose of getting all the slots, at least in perfectly clear way. ...and I should start work on the HUB feature asap.