I see many similarities as people hiring servers for mining, AMD video cards with better performance than the NVIDIA
Processors having good results.
Finally, from a technical point of view, the algorithms are similar in some way?
No they are very different
As stated there are many differences, and I think the only similarity is that both try to have stealth or anonymous transactions.
Cryptonight is more oriented to do 2 MB allocations for hash, something that most modern CPUs (Computer Processors) can cache directly, so CPU mining is excellent for it. Also they claim that since GPUs (Graph Cards) and ASICs (Dedicated Chips for functions like mining) do not have this CPU memory cache so either would be very expensive or just not viable trying to make mining more fair.
Look more in here:
https://cryptonote.org/inside.php#equal-proof-of-work
For ZCash (Equihash) it is a fact that the Sol/s are higher with faster GPUs… even if, and I quote: “Equihash is a memory-oriented Proof-of-Work, which means how much mining you can do is mostly determined by how much RAM you have. We think it is unlikely that anyone will be able to build cost-effective custom hardware (ASICs) for mining in the foreseeable future.”
I have 2 GB GPUs and 4 GB GPUs and I do not see that as a factor. Also, making ASICs with this kind of RAM memory should be very simple and unexpensive vs ASIC Memory Cache.
In my case, I have my CPUs mining for Cryptonight algorithm, and my GPUs for Equihash.
Hope this helps.