We see the mention of a freshwater lake of 167 km square in Israel called as the Sea of Galilee or the Sea of Tiberias at Mtt 4:18, Mtt 15:29, Mk 1:16, Mk 7:31 and Jn 16:1. I wish to know the logic behind calling a lake a sea.
This is not an unusual usage, nor one that needs a specifically religious explanation. "The Sea of Galilee" is the standard English translation of the original Greek θάλασσαν τῆς Γαλιλαίας ("thalassan tes Galilaias"); that is, "the θάλασσα of Galilee"). One sees this usage, for example, in Matthew 4:18.
Liddell and Short, a commonly used Greek-English lexicon, defines θάλασσα as "the sea", using primarily references to the Mediterranean.
Merriam-Webster gives a usage of "sea" to mean
a great body of salt water that covers much of the earth
that is, a synonym of "ocean". However, it also describes "sea" as used to mean
an inland body of water—used especially for names of such bodies
It is in this sense that the body of water you mention is called "the Sea of Galilee".
θαλλω, thallo, Strong 330 is the Greek word used in relation to plants, that they 'flourish', as described in Thayer's Lexicon. It may well be that the word was used, not of individual plants, but of fields of growing crops.
A field of flourishing corn or wheat, stretching out before the eyes, moving and rippling in the wind, appears like a body of water.
Thus the word θαλλασσα, thallassa, may not refer to the size of the body of water, it may just refer to the characteristics of a large body of water in the way it appears and in the way it moves.
The θαλλασσα (the 'sea') of Galilee at 33 miles (see Wikipedia) is large enough to have an horizon. Which only requires a distance of about three miles, when viewed at ground level (see Wikipedia). One cannot see the farther shore. Thus 'sea' seems, to me, a perfectly correct translation.
It is a body of water, moving in the wind, rippling like a field of standing corn, and stretches as far as the eye can see.
If this derivation and interpretation is correct, then it would have implications in those instances where it is mentioned in scripture - the underlying meaning of flourishing crops and plentiful supply of food.
And there may well be a spiritual allusion in the fact (as reported by Wikipedia) that the sea of Galilee is freshwater, so crops could flourish right up to (and, possibly, into) its very waters.
It's fairly simple. The Sea of Galilee is the second lowest body of water under sea level. The lowest is the Dead Sea.
The reason they are called "seas" is because of their salinity content. In the Sea of Galilee's case, the weight of the fresh water suppresses the salty springs under her.
[because of the drought and lower lake levels] In February 2018, The city of Tiberias requested a desalination plant to treat the water coming from the Sea of Galilee ... -ibid-
The Sea of Galilee is at risk of becoming irreversibly salinized by the salt water springs under the lake, which are held in check by the weight of the freshwater on top of them. -idid-
At the same time, the brass laver in Solomon's temple is also called the sea.
And the pillars of brass that were in the house of the LORD, and the bases, and the brasen sea that was in the house of the LORD, did the Chaldees break in pieces, and carried the brass of them to Babylon. 2 Kings 25:13
So, it's not like the wording of sea is a definitional or geographic error of distinction.