Of course not. I just think the threat if the government straight-up lie and then abuse the contact graph is obvious and not particularly interesting as a conspiracy theory.
I also think that in this particular case, it's not really that much of a threat, for the simple reason that more effective means are already trivially available for the government to track people using their mobile phones if it wants to.
The problem is they're not straight-up lying: they're admitting to MPs that this data will be used for "research", people will have no right to delete their own data, and that Peter Thiel's Palantir is involved and basically giving away the services for free.
Whataboutmanship isn't an excuse either, to me. Just because the government is capable of hacking our phones, getting our phone records, and sending men in black cars to watch our houses doesn't mean we should also invite them in via an app we choose to install.
Edit: I agree with you: I don't think this is a conspiracy and I don't think a centralised contact tracing app is a security concern if its used just for that.
However, I do not trust the British government at all, especially given their beyond-satire record. Don't give the state an inch: they'll take a mile.
I also think that in this particular case, it's not really that much of a threat, for the simple reason that more effective means are already trivially available for the government to track people using their mobile phones if it wants to.