People use a wide definition of slavery, so of course you can call a yearly debt of work, by the peasants, to the Pharaoh, slavery. Just like people today call working for "the man" wage slavery. There are certainly different types of slavery. For example, some slavery has the ability for the slave to work their way into a society/freedom and show that they can assimilate, and some are slaves for life along with all children they make.
Saying slaves did not build the pyramids is not saying slavery didn't exist in Egypt at the time, it's saying that the archeological evidence in the camps in which the pyramid workers lived matched, more closely, that of the "free" peasant class, and not the living conditions of similar slave quarters found elsewhere of the time. Furthermore, Egypt was fairly contained nation for a long time, in which they could not expand to bring in masses of slaves that would be needed to build such huge monuments.
I think there is a lot of Roman slavery methods that get conflated with other slavery methods around the Mediterranean, especially when one remembers that we live closer in time to Cesar, than he lived to when the pyramids were built.