One possible explanation is that buyers don't want price to go up [yet] because they are still buying.
Either way, on exchange or off, if they are long term, it's good news since the available float would be reduced, again, IF they are long term.
On the other hand, if they want to crash the market, they'd better be really good because that is a costly operation that could easily backfire.
I agree that buying a large sum on the OTC markets is probably because they don't want the price to go up.
But I don't know if it's such good news even if 'long term'. We must remember these people are sharks and we would be foolish to think that they would buy in for X amount and just sit and wait for the price to go up. I consider it much more likely that they would get a sizeable position in the market, and then follow up by playing the market in order to increase their stacks. You mentioned long term vs short term, and I'm not sure there's a difference.
Short term simply wanting to crash the market makes little sense, unless it is in order to buy it all up cheap which would make them a long term investor rather than short term. I doubt any party would simply throw billions 'just to kill Bitcoin'. After all, profit makes the world go around. But if there's profit to be made by crashing Bitcoin, then buying it all up for cheap, then I definitely think they're going to try it. It wouldn't be costly if it turned out to be the most profitable thing ever. And what's a few billion here and there, for these kind of people?
There are only 21 million eventual BTC possible (and that number is even lower given lost BTC over time) and it wouldn't take much from serious long term investors to push price higher on a sustainable basis. Long term types are usually very smart at this stage of a great long term investment (you have to be in order to be at the right place at the right time) and their buying habits are quiet savvy. I'm confident that strong hands are accumulating BTC, and other quality alts, for the long term.