Intel is merely the manufacturer of the networking hardware itself. Intel doesn't make computers under their own name besides the NUC. Any other computer or device manufacturer could choose to use an Intel chipset for their networking. While you may not have laptops, desktop PCs frequently do have Intel chipsets.
Are you sure you were talking to a real Telus rep? None of that makes sense. Wifi definitely has less than a 1 block range. You'll be lucky to even get reception in most cases when you're outside your home or yard. Having to use the wireless boosters is proof of that. Hidden wifi networks can be easily found. Any device connecting to the Telus router will have its MAC appear in the log.
Not all MAC addresses are going to show up in a search. It depends if the device is from a manufacturer that registered the first six characters of the MAC address or not. There are also some other devices where people can manually change the MAC address. Another thing to be aware of is that many devices have more than one MAC address. One for wireless, one for wired and in some cases more additional ones depending on the hardware.
If you are really worried, change ALL of your wireless network names and passwords. It will be a headache at first but it would make it harder for unknown devices to connect. As long as you are the only person with the password, you can limit who or what device has access. For your ex, you could even set up the guest wifi with a separate password and isolate it so anyone on the guest wifi cannot access anything on the rest of your network.
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