Is a company issuing its own stock (i.e. selling) also market manipulation? It brings the price down. Buyback is the reverse operation.

The difference from actual price manipulation, is that the price change in issues and buybacks is a permanent effect of the material change of the number of outstanding shares, not a fledging effect of the change in trade volume, i.e. the intrinsic value of the stock goes up or down.

edit: of course buybacks, like dividends, decrease the value of a company, and issuing stock increase it, so it is not clear cut.