They are going to spend the company's cash reserve buying back stock and artificial restrict supply which will raise the price?
Insider buying is when the insiders themselves spend their own money on the stock. It's very difficult for them to successfully manipulate it upward--if they buy e.g. 5% of the outstanding shares, then to profit from their manipulation they have to sell 5% of the outstanding shares. The net result is likely to be that the stock ends up where it was, and the insiders have just paid their brokers a lot of money.
Also, what's artificial about this? It seems natural to me that if there are fewer shares outstanding, the price per share would go up (unless the company was knowingly buying them back for more than they're really worth). And "artificial" restriction in supply would be something like paying a group of shareholders not to sell for a certain period, to reduce the number of tradable shares. That stuff's usually illegal.
Other investors are often supportive of this as it gives them a profitable exit from the soon to rise stock.
On its own, less supply leading to higher prices is perfectly natural.
Imagine that there are 3 partners each owning a 1/3 interest in a firm. If the firm decides to buy out one of the partners with company money, and that the partner agrees to this, this leave the other two with a 50% interest in the company. Nothing wrong with that at all and nobody has been forced to do anything it doesn't want. It's not artificial, the stock prices are higher because each share is now a bigger piece of the comapny.
You just reduce the number of slices of the pie, so that each slice is a little bigger. There's nothing nefarious about it, it's one of many valid ways to allocate capital as long as they buy the shares at fair valuation (or better, when they are undervalued). You usually do that if you wouldn't get a higher return by putting that money to work somewhere else.