That's not just a bit weird freddie! They nicked your wedding date and venue
I can laugh about it now, but it was odd at the time. We didn't know the full extent of it either, we were told other stuff by other friends later on - one friend who I'd spent the day shopping with once said she'd almost interrogated her about what shops we'd been in and what I'd bought
I don't know why they did it, all our friends knew the date we had chosen as we had openly discussed it as it was a special date for us. All our friends said keep the date and they'd come to our wedding anyway, but we didn't want to get involved in a date war - still niggles me a bit though 11 years later 
She had her own style which was totally different to what I wore so it was a bit disconcerting to start seeing her in exactly the same clothes, their house was a totally different style to ours which over time became pretty much a replica of our house, then the same car - exactly the same - same year, same cc, same colour
After the wedding thing, we withdrew a bit and then we moved away about a year after we got married and apart from the odd hello on Facebook we don't have any contact with them now. Another friend of ours had a child in the same school as theirs for a while and I vaguely remember there being some oddness with another couple, but our friends have moved away too now, so we haven't heard from them for a while
I've no idea why us, I'm no style queen, our house interior didn't come from Homes and Gardens or anything and our wedding venue wasn't The Ritz or anything. The DH was an old school friend of my DH. Very odd