The 4021 and 74LS165 are similar, inasmuch as they're both PISO shift registers, but they're not the same part. Here's representative datasheets for both parts from TI:

http://www.ti.com/lit/ds/symlink/cd4021b.pdf

http://www.ti.com/lit/ds/symlink/sn74ls165a.pdf

I don't think the differences are relevant in this application, though.