Can the BTCitcoins of a wallet be stolen just with the public key?
Yes. Absolutely.
The Public Key is mathematically related to the Private Key by an algorithm. If you get the Private Key, you can steal the Bitcoin. Just work a little bit to discover the algorithm which converts the Public Key to the Private Key and you are totally golden. First one to discover it is a millionaire!!! But don't be greedy. If others find out you did it, the whole system will get less valuable fast.
The statement is irony. I slowly believe in your thought but I think if it is possible then bitcoin already gone right now. Public keys have similarity in private keys but you cannot unlock or encrypt easily the algorithm provided by just using a public key. Even a mathematician and hacker will combine their knowledges, they can't solve and cracked bitcoins algorithm unless you are Satoshi Nakamoto.