So was the developer tested this deliberately or was it an accidental mistake.
I don't find any issue with it, either it was done mistakenly or deliberately, or maybe that miner might be testing or showing off to a newbie that the BTC blockchain can not be tricked.
It seems to me if I do exactly what the developer did a could case an invalid block correct?
It will definitely, be the issue was an orphan transaction.
Making 35 invalid blocks in a day vs 1 if so can this fuck up the block chain speed?
I don't think so, because the blockchain speed depends on the valid blocks, not on the invalid blocks, because invalid blocks will not be allowed to enter the house of the blockchain and will be removed from the door. But it will be a waste for the miner, as the miner will be wasting resources on the invalid block which after spending some sources tagged as invalid.