Is it true that the Electoral College forces the US to only have two real political parties?

No.... but in a way it discourages third party participation. Since most states are winner take all unless a third party candidate can win a majority of votes in a state they will get zero electoral votes. Case in Point: Clinton vs Bush: Ross Perot received 19% of the popular vote and zero electoral votes. Clinton was elected despite receiving only 43% of the popular vote. The victory appeared lopsided because Clinton won 32 states and DC for 370 electoral well over the 270 majority required. With the current electoral college make up it is unlikely there will never be a successful third party candidate.