That is NOT true, to the extent that Glock parts will interchange on Glock pistols. For example, a Glock 23 40 cal slide (or a Glock 32 .357SIG slide) will drop right on and function correctly on a Glock 19 frame, but when Dagger owners (including "yours truly") have tried a Glock 23 top half on a Dagger frame, the slide can be forced into place, but it will NOT function (the Dagger trigger bar interferes with & binds the slide). You can get it functioning by modifying or replacing the trigger bar, but either approach voids the PSA warranty; in fact, adding ANY non-PSA parts voids the warranty.
The common perception of the phrase "Glock compatible" is based on experience with Glock handguns, which includes the ability to interchange Glock factory parts on Glock frames, and the ability to use aftermarket parts designed for Glock factory handguns. The PSA Dagger is only partially "Glock compatible", and it's worth knowing that before you buy the PSA product. And FWIW, I'm a long-term PSA customer, and recommend the company & its products to my friends (although some of their products have limitations ;^)...
As always IMHO, YMMV, FWIW, etc., etc...