No, it refers to bottom bracket shell width of the frame.
The axles come in lengths to suit 65, 68, 70 and 74mm bottom bracket widths.
There is usually another number stamped on that gives overall length of the axle, plus a letter (or two) stamped on also which tells you the intended purpose of the axle.
For example 'P' for Pista (Track), 'S' (or 'SS') for Strada(Road); occasionally there will be a 'C' for Cyclocross.
I see your example seems to just say "70", and nothing else, which suggests it may be Italian or French as British BB's tend to be 68mm.
Here's a guide to axle length that might help you determine what you've got.....
View attachment 1549084
I'm not knowledgeable enough to give you a date, sorry