Unless you're all using ethernet-over-powerline technology such as HomePlug, I'd say it's highly unlikely. Your system has to actually interpret any data sent to it, which it shouldn't do unless it's designed to.
On a laptop, your power cable contains a switched-mode supply that regulates a DC voltage supply from the AC voltage supplied by your mains. This means that any signal or noise on the mains line is destroyed before it even reaches the laptop. The same type of supply is used on desktop machines. Even if an attacker generated large amounts of noise on the power line, the regulators in your power supply would entirely remove it, or shut down to protect your system.
If you've been infected, I'd guess you caught the malware over their network instead. If you connect to their wireless network, the malware on their machines might attempt to exploit various vulnerabilities on your system via the network. This can be mitigated by enabling your firewall, installing all OS and software updates, and limiting access to any network shares you provide.