In this Lieberman is wrong. Egypt's treaty with Israel required it to provide Israel with unrestricted purchases of oil extracted from the Sinai. As those oil resources were depleted, the treaty was amended to substitute natural gas, which Egypt is bound to supply. So yes, they're in violation of the treaty. The Egyptian company is separately liable as Israeli companies partly funded construction of the gas pipeline. Either they supply gas or the Israelis are owed compensation.

"normalization of relation" included in the peace treaty is vague term; it may or may not include supplying Israel with fuel WITH the NORMAL MARKET Price as NORMAL selling of gas to countries other than Israel. Egypt is ready to resupply Israel with gas after NORMAL FREE negotiation of the price.