Well, it can, if games 6 and 7 generally draw more viewers, which would increase the average. (EDIT TO ADD: Here's a link that says the overall series viewership is down 25% from 2017 -- but just down 14% based on the first 5 games: http://www.sportsmediawatch.com/2018/10/world-series-ratings-decline-third-lowest/ ) I got hung up on this line a bit: "the overall average-minute audience of 198,000 is up 9% from 2017’s seven-game average of 182,000." But it's in the paragraph about streaming, so maybe that is just streaming numbers? But, a drop from 2016 and 2017 isn't a great barometer of anything, because 2016 and 2017 were recent high points. An average of 14.3 million viewers puts 2018 right in line with 2008, 2010, 2012, 2013, 2014, and 2015, according to this chart:
We all know modern TV ratings are down for all kinds of things, including MLB. There's nothing in this 2018 data that suggests MLB's ratings are continuing to sink lower, much less sinking lower at a faster rate than other programming.