The phrase "parallel processing" is used very loosely in different contexts. It is true that humans have taught machines they built to do certain parallel processing and it is possible for the machines to function like that because we built their parts with that in mind. Whatever electronic control is residing in them is also implanted by us. Therefore co-ordination of their activities is also possible to be parallel as we designed them to be so. Machines handle volumes of data better at a time.

But if you think about it, most of the times, when we say we are doing these 3-4 things parallelly, we more often than not mean we will do all these things in a certain time frame in no necessarily particular or some sequence. Humans by nature do 1 thing at a time, even though they have complex capabilities of prioritization, planning, qualitative comprehension etc. in general, compared to machines.

However, very seldom is it actually "parallel processing". It is at best, (consciously or sub-consciously) planned sequential processing which we refer to. I mean the only realistic parallel processing I can think of, is some circus performers are probably capable of some active parallel processing in their stunts. In most other cases, it is one active processing accompanied by some background processing, at best.