Is it possible that one person or group fake the whole BCN blockchain to make
it look like BCN has been mined by many computers for almost 2 years?

Not that many computers. Could be done in a relatively short time with a server farm or botnet.
Even now this coin is pretty small and the difficulty is much higher
I think it is more likely that the developer or a small team bumbled along for two years and then later decide to try to cash out the premine with a pump-and-dump instead of starting a new coin. That may be behind the split between bytecoin and cryptonote. All of this is speculation, but I'm trying to fit the facts as well as possible.
There are major flaws in that logic. If it was for profit then they would go the monero route with a smaller supply making it an "investment" currency rather than a means of exchange currency. If you read anything about them instead of trying to cash in on monero it's not one developer or small team and the hashrate is in the blockchain along with transactions showing it's being used and there is much too high of a hashrate for a "small team" to be just bumbling along.
It would make sense that the people interested in developing an anon crypto wouldn't be looking to make an very limited supply speculative investment style crypto people would want to horde rather than use. It also makes sense that someone looking to cash in would go for a more limited supply to help push the value. Doesn't make sense to develop BCN to cash in on early mining. Also hard to believe the motivation behind developing an anon currency is to cash in on easy early mining..the motivation to create cryptos isn't to make miners and early adopters rich. The logic behind them wanting to pump this to dump their mined coins and a small team owning all 80% doesn't hold up.
Why it was developed and launched in such secrecy I can't answer. I suspect this very well could be a proof of concept coin and not a polished coin meant to be released to the Joe public. If they were looking to pump and dump the test coin, why not do it with a flashy website and polished wallet followed by an ANN thread here. For intelligent people it wouldn't be hard to produce a better scheme to cash in if that was their objective with Byte.
I have no problem with Monero and think it's price appreciation and being launched on bitcointalk will help adoption and use of crytponote and privacy in general for cryptos. It is and was one of Bitcoin's keys to success. It's obvious you're into cryptos to make money not much else which is fine, but why do you need to try and plant doubt about the motivations behind Byte coin to pump you investment in monero? If you don't have confidence in Monero to stand on it's own merit then why invest in it at all?