Linguistic connection between the geophysical "bluff" and the deceptive "bluff"?

The deceptive bluff comes from the Middle Dutch bluffen meaning to swell or brag.

The geophysical bluff comes from the Middle Low German blaff meaning smooth.

Perhaps they may be related through the process of the wrinkled surface of something which is inflated becomes smooth.

If one actually bothers to read the Etymonline entry linked by the OP:

bluff (v.) 1839, American English, poker term, perhaps from Dutch bluffen "to brag, boast," or verbluffen "to baffle, mislead."

bluff (n.1) "broad, vertical cliff," 1680s, from bluff (adj.) "with a broad, flat front" (1620s), a sailors' word, probably from Dutch blaf "flat, broad."

They both come from Dutch, but that's about all they have in common.