Could the camera be wrongly adjusted.
It's highly unlikely that the camera recorded your speed inaccurately. They're very closely monitored both in-house and independently. A physical/hardware fault with one particular unit would be caught extremely quickly. A software issue causing incorrect calibration would be widespread and easily flagged.
No technology is 100% infallible 100% of the time, but the the technology behind measuring your speed is extremely robust and the chances of a one-time freak calibration malfunction catching you out are ridiculously slim.
For context - The largest known speed camera glitch in the UK was identified last year, believed to have been caused by a software update to the around 150 cameras that interact with variable speed signs on motorways and A roads. The fault wasn't with the cameras themselves, but the way in which they communicated with the signs.
Essentially there was a delay of a few seconds between the variable speed signs updating and the activation threshold of the cameras following suit. So a sign might have changed from 40mph to 60mph, but anyone unlucky enough to have increased their speed above 40 in that brief window would have activated the camera.
The glitch was active for around 4 years; the only reason it wasn't caught sooner is that it was so rare. The affected cameras were activated over 6 million times during that period - of those activations only 2500 were caused by the glitch, and because not every activation leads to enforcement action, even fewer resulted in bogus prosecutions.
can they set it wrongly deliberately to catch people?
Even if we look past the issue of how they'd manage it without getting caught...why would they? Can you imagine the fallout when it inevitably came to light? It'd be bigger than the Post Office scandal, and that was caused by faulty software, not deliberate, malicious fraud.
Whether it was a national/force-specific directive, or a case of rogue individuals being able to adjust the hardware/software without detection, it would bring down the entire system. Not to mention the wider impact it would have on policing and the justice system.
When the glitch above was identified, they didn't just stop using the affected cameras, they paused the entire variable system. They cancelled all ongoing historical prosecutions involving all variable speed cameras and cancelled almost 40,000 speed awareness courses, regardless of whether they were impacted by the glitch or not. The small number of people actually prosecuted are having their fines refunded and points removed from their licenses, and will receive additional compensation from the government (as they should, not just for the hassle but more tangible issues like raised insurance premiums).
Imagine what they'd have to do if they were caught issuing fraudulent fines on purpose, just to bring in a few extra quid. It's an old conspiracy theory, and like most of them it doesn't hold up to scrutiny. The wider impact simply wouldn't justify the pocket change it'd raise.