This is an on-off switch, identical in function to a top-actuated DIP switch. The datasheet doesn't explicitly state that, but the listed typical applications are a clue: "Address switch for industrial controls" and "Logic switching for computers and peripherals" would not ordinarily use a momentary switch.
Datasheets will call out "momentary" or "MOM" for a momentary switch. Another convention is to use parentheses to denote a momentary function. For example OFF-ON and OFF-(ON) would indicate two switch variants, with the latter being momentary.
I have never seen a momentary switch of this type. The best I can suggest is a tactile pushbutton switch.