Actually, according to the Hagaddah, it's that the Jews were slaves in Egypt and built cities for Pharaoh: Pithom and Raamses. No info on pyramids.
I was watching something, might've been on The History Channel (creeping senility prevents further identification thereof); their theory was that the Hebrews were probably folk tossed out of Egypt for some other
reason, then they met up with the Canaanites who really were ex-slaves, and instead of conquering them (a la the Joshua story, with the walls of Jericho coming down, yadda yadda), they intermarried.
Given that the Bible has multiple creation myths, to my mind it kinda makes sense that the earlier version (1.0?) of the Israelites would be a mix of peoples. I love how people look at the Bible as a historical work or even a scientific (ha!) one, but the reality is that it's one big advertisement for the religion. E. g. here are a bunch of stories showing why this is the better way versus those cow-worshipping folk down the street, and here's what happens when you screw up, and here's how heroic and righteous our people are, so why not join up?
That way, you can kinda combine the expulsion of problematic people (the Hebrews) with what was perhaps even a voluntary manumission (the Canaanites) and convert it into a heroic/religious slave revolt story whereby not only do the Israelites look good but it also furthers the whole overarching plot line of: here's our faith, we're #1!
And don't get me started on Pharaoh in Exodus. After the Red Sea goes back to the way it was, and all of the army, horses and chariots sink to the bottom, he's left to go back to Egypt, which is starving and demoralized and sick, and explain himself. If Pharaoh's got any sense, he either flees to Midian or elsewhere and goes into the archaic version of The Witness Protection Program, or he commits hara-kiri. Otherwise he's setting himself up for, if he returns to Egypt, being torn apart by the populace with the last of the strength that they've got.