Doesn't mean a lot. For starters, mechanical engineers have such a huge array of jobs that they feed into that this is barely a drop in the bucket. It is more important for aerospace engineers, but most of the cuts (at least at Boeing) are in management. For the most part they are leaving the engineering staff intact, so it probably still won't be that big of a deal.
On top of that, Boeing has an absolutely booming commercial venture right now. They are finally pumping out 787 deliveries like crazy, they have taken orders for almost 1000 new 737 MAX planes over the past year and a half or so, and are in the process of designing the 777 MAX, which will likely sell like hotcakes too. That business is booming.
The aerospace industry in general is volatile and has ups and downs, particularly on the military side of things. The spending climate in Washington right now dictates that there aren't going to be a lot of military planes being purchased in the immediate future. That said, it will come back up eventually. Boeing and I assume Lockheed are both working on their 6th-generation fighter aircraft, for example, because it will come back around eventually.
Overall, Boeing is in much better position right now than Lockheed on the strength of its commercial side, which is not feeling the penny-pinching in Washington. Lockheed doesn't have that to fall back on.