Can one arabic speaker not understand what another arabic speaker said?

The American who spoke Arabic cannot understand when I say:" Motashariff Bilikayik" or "Kayfa Haluk" to them. Motashariff Bilikayik = Nice to meet you Kayfa Haluk = How are you? Arabs from Libya and Egypt understood when I say those phrases to them. What is going on? Are they pretending not... show more The American who spoke Arabic cannot understand when I say:" Motashariff Bilikayik" or "Kayfa Haluk" to them.

Motashariff Bilikayik = Nice to meet you
Kayfa Haluk = How are you?

Arabs from Libya and Egypt understood when I say those phrases to them.

What is going on?

Are they pretending not to understand or are they just don't understand the dialect?
Update: When I say "Akhi" for "my brother" and "Akhta" for "my sister", the Syrian understood it and Libyan understood it also. Again the Americans speaking Arabic cannot understand my Arabic, and corrected me saying its "Akh" and "Ukh" for brother and sister.
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